Architecturally Design Mortar Base Plate

ABSTRACT

An architecturally design mortar base plate is provided having an architecturally design structure having a center receiving hub and socket made of one piece machine from solid steel for socket to absorb the impact over repeated cycling. A plurality of forged metal ribs extend radially out therefrom to distribute the impact strength from the socket regime to throughout the whole base volume to consume the energy that created due to firing.

RELATED APPLICATIONS

The present application incorporates subject matter that was first disclosed in U.S. Provisional Application 61/182,455 filed on May 29, 2009 and U.S. Provisional Application 61/239,219 filed on Sep. 2, 2009, which are incorporated by reference herein as if fully rewritten. There are no previously filed, nor any co-pending applications, anywhere in the world.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to lightweight mortar projectile guns and, more particularly, to an improved architectural design for a motor base plate.

2. Description of the Related Art

Lightweight gun systems are being widely used in current military operations. The lighter the gun, the greater the mobility and versatility in maneuvering the military force has. This is of an advantage where the gun systems must be transported quickly, or to difficult terrains or climates. Modern mortar systems have been an effective means of force suppression since the trench warfare of WWI. Their evolution over subsequent years has led to improvements in safety, range, and lethality. A recent unclassified debriefing from soldiers in Afghanistan noted that mortars were “essential” due to the distance and elevation to targets in the mountainous terrain, and that “mortars were responsible for many kills”.

Mortars and their ammunition are smaller and lighter than other artillery, making them ideal for support of movement to contact, ambush, retrograde, and other deployment maneuvers. Their “lobbing” trajectory can place their munitions on target over obstacles and to positions at higher elevations than the position of the mortar. The smooth bore of the mortar tube eliminates loads created by the rifling of a gun tube, allowing mortar rounds to carry higher payloads in thinner skins than artillery shells, thus providing a greater explosive source than similar sized artillery.

Unlike artillery pieces such as howitzers and cannon, mortars need no complex recoil equipment and are usually smoothbore and muzzle-loaded. The recoil force of the mortar is transferred directly into the baseplate and from there into the ground. The metal baseplates are relatively heavy:

-   -   M7 baseplate for M224 60 mm mortar—14.4 lbs     -   M3AI baseplate for M252 81 mm mortar—29 lbs     -   M9 baseplate for 120 mm mortar—136 lbs

FIG. 1 illustrates a 120 mm mortar assembly currently in use. Mortar assembly 2 includes barrel 4, breech piece 5, bipod 6, and base-plate 8. Barrel 4 is angled up and down to shoot the round at the desired trajectory. The lower end of the barrel 4 is externally threaded to take the breech piece 5. The breech piece holds the striker. The striker is a fixed stud on which the bomb falls under gravity. The lower end of the breech piece is shaped into a ball (not shown) which enters a socket in the base plate 8.

Bipod 6 functions as a support and means to adjust the angle of trajectory. This is achieved by adjusting the angle that barrel 4 makes with the ground. It also provides the means to hold barrel 4 at a proper angle. Base-plate 8 is a heavy welded steel dish. It has socket 10 at the center to take the breech piece. This provides the capability to rotate the barrel 4 around a full 360 without shifting the base-plate.

Similar to base-plate 8, barrel 4 and bipod 6 are also made of steel. Current mortars take advantage of important attributes of steel. However, there are disadvantages associated with the use of steel as the main material for manufacturing the mortars. For example, 81 mm and 120 mm mortars made of steel are very heavy and require a team to transport each piece. Typical prior art 120 mm mortars weigh between 272 kg and 341 kg in the traveling configuration. This creates problems when these mortars can no longer be carried by machine and must be carried by humans. In these situations, the 120 mm mortars must be dismantled and transported part by part. This requires at least 3 to 4 people to carry all the parts. Furthermore, in situations where time is of the essence and the rounds must be fired continuously, dismantling and re-assembling the mortars may not be practical.

Another problem with the current 120 mm mortars is that there is no mechanism to reduce the recoil force and absorb the recoil energy of the mortar assembly after each round is fired. Presently, sand bags are placed under and around base-plate 8 to absorb the recoil movement of mortar 2. Despite this, present 120 mm mortars on a non-absorbing surface may jump as high as 3 to 4 feet off the ground. This poses a clear danger to the mortar operators. As a consequence, mortars are either placed on absorbing surfaces such as soft ground or sandbags and may have extra bags placed on the mount to reduce rebound effects. The recoil problem is even greater with a light mortar such as the mortar of the present invention.

Previous attempts at achieving weight reduction have focused on simple material substitution, without significant structural changes in design to effect a meaningful weight reduction. In addition, the materials presently used in the mortar base plates are susceptible to stress corrosion cracking due to the combination of operating environments and residual stresses created during manufacturing processes or stresses encountered during operation.

Consequently, a need has been felt for providing an mortar gun system having a light weight, portable base plate capable of withstanding repeated, substantial recoil force and absorb the recoil energy of the gun system caused by firing rounds.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an improved motor base plate capable of handling recoil impact stress to achieve all the military qualification stress levels for all available mortar base plates.

Features of the present invention are provided in an architecturally design mortar base plate that is light weight, and cost effective and size insensitive such that it can be adapted to meet any available mortar base, such as 60 mm, 81 mm, 120 mm or any size between.

Briefly described according to one embodiment of the present invention, an architecturally design mortar base plate is provided having a forged metal frame structure having a center receiving hub and socket made of one piece machine from solid maranging steel, 4140 Steel, or any structural material for socket to absorb the impact over repeated cycling. A plurality of metal ribs extend radially out therefrom to distribute the impact strength from the socket regime to throughout the whole base volume to consume the energy that created due to firing. The metal ribs interconnect in an interlocking, nested, mounted, bonded or welded manner to support the socket in a position that is repeatable after firing. The ribs further are architectural designed to minimize weight while maintaining maximum desired strength.

Advantages the present invention result from the optimizing of strength in a manner in which the overall material volume is reduced, thereby reducing the total weight of the mortar base plate itself. The required strength comes from the choice of material and composite design. The whole design is based on eliminating stress corrosion or any weakening mechanism of the existing bulk materials that are used for such hardware. The mortar base is designed such way that the critical cracks are engineered not to grow and controlled by the geometry, several and different material choice and engineered design to eliminate or minimize the crack formation and crack growth during life of the base plate.

Further, the use of the “spider” configuration and stabilizer pad provides a platform that dynamically attenuates the force of the mortar recoil over time in much the same manner as recoil adapters on aircraft mounted gun systems. This reduction of load during the firing period will provide a more stable firing platform in soft ground or snow conditions.

Further still, the structural design and material properties of the improved baseplate will substantially increase the useful life of this mortar system component compared to the existing aluminum and other potential substitute materials by utilizing a more impact compliant structure with a configuration that eliminates high stress-concentration members such as gussets.

Additionally, it is a goal of the program that the proposed mortar baseplate design, with replaceable, interchangeable 60 mm and 81 mm ball sockets, will be strong enough and light enough to replace both the M3A1 and M7 baseplates, thus significantly reducing logistics costs.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features of the present invention will become better understood with reference to the following more detailed description and claims taken in conjunction with the accompanying drawings, in which like elements are identified with like symbols, and in which:

FIG. 1 illustrates an example of a PRIOR ART mortar system;

FIG. 2 is a perspective view of a support leg structure of an architecturally design mortar base plate according to a preferred embodiment of the present invention;

FIG. 3 is a top plan view thereof;

FIG. 4 is a cross sectional view taken along line IV-IV of FIG. 3;

FIG. 5 is a top plan view thereof shown in conjunction with a ball socket 14;

FIG. 6 is a cross sectional view taken along line VI-VI of FIG. 5

FIG. 7 is partial perspective view of a ball socket 14 for use in conjunction with the preferred and alternate embodiments of the present invention;

FIG. 8 is a cross sectional view thereof;

FIG. 9 is a perspective view of an architecturally design mortar base plate according to a first alternate embodiment of the present invention;

FIG. 10 is a top plan view thereof;

FIG. 11 is a side elevational view thereof;

FIG. 12 is a side elevational view of the internal structural skeleton for use therewith;

FIG. 13 is a cross sectional view taken along line XII-XII of FIG. 11;

FIG. 14 is a detailed elevational view the internal structural skeleton element for use therewith;

FIG. 15 is a top perspective view of a stabilizer pad 200 for use in conjunction with any embodiment of the present invention;

FIG. 16 is a cross sectional view taken along line XVI-XVI of FIG. 17;

FIG. 17 is a top plan view thereof;

FIG. 18 is a bottom perspective view of the stabilizer pad 200;

FIG. 19. Is a cross sectional view taken along line XIX-XIX of FIG. 20;

FIG. 20 is a bottom plan view thereof;

FIG. 21 is a diagram of a Baseplate Assembly Loads During Mortar Firing; and

FIG. 22 is a Finite Element Analysis of a Support Leg 20.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The best mode for carrying out the invention is presented in terms of its preferred embodiment, herein depicted within the Figures.

1. Detailed Description of the Figures

Referring now to FIG. 2-8, an architecturally design mortar base plate 10 is shown according to the preferred embodiment of the present invention for use in conjunction with the M252 81 mm mortar. The base plate 10 is designed to replace base plate 8 of the PRIOR ART as shown in FIG. 1. FIG. The base plate 10 is formed of a composite architectural structure having a center receiving hub 12 and forming a connection point for a socket 14. The hub 12 is made of one piece machine from one piece machine from solid maranging steel, 4140 Steel, or any structural material for socket to absorb the impact over repeated cycling. A plurality of optimized metal ribs 20 extend radially out from the hub 12. The ribs 20 are forging integrally to shape metal by using localized compressive forces. Such forging additionally decreases corrosion or stress cracking weaknesses by eliminating voids in the material that facilitate such weaknesses or failures. As would be obvious to a person having ordinary skill in the relevant art, in hindsight of the teachings and benefits disclosed by the present invention, the present invention can be readily adapted to cold forging, warm forging or hot forging. Cold forging is done at room temperature or near room temperature. Hot forging is done at a high temperature, which makes metal easier to shape and less likely to fracture. Warm forging is done at intermediate temperature between room temperature and hot forging temperatures.

The primary support of the baseplate consists of a structurally engineered multi-legged unit. The design concept shown in FIG. 3 is an illustrative example of the supports forming a 6-legged hexagonal pattern. Other patterns involving different numbers of legs, and some leg angles of unequal values, will be considered during the initial evaluation.

The structural design of the support leg structure 10 gives it the characteristics of a spring, which will absorb and distribute the recoil force of the mortar. The legs will be fabricated from materials that optimize the weight to stiffness ratio for the application. While maraging steel is known to possess superior strength (typically 3 times greater than that of heat-treated alloy steel, such as 4140), toughness, and malleability, characteristics that provide the least weight for a given strength. Non-stainless varieties of maraging steels are moderately corrosion-resistant, and resist stress corrosion and hydrogen embrittlement. Additional corrosion protection is gained by cadmium plating or phosphating. Another unique characteristic of the maraging steel is that even though it has a very high yield strength and fracture toughness, the fracture mechanism is ductile which is very unique property of the material. This characteristic of the steel enables engineers to design critical structures—such as ballistic missile skins—that are significantly lighter and stronger than with other materials.

Fabrication of the support leg structure will consist of machining a flat pattern of the structure from steel plate. The part will then be press-forged into its final shape.

It has been found that the functional requirements for the mortar baseplate include: transmitting the recoil force to ground in a manner that does not shift the mortar cannon prior to exit of the projectile; withstanding the recoil of a minimum of ten thousand rounds without permanent deformation, fracture, or other failure modes; and, operating in specified environmental extremes of temperature, humidity, precipitation, particulates, etc. A typical force-time curve for a projectile launched by a non-progressive propellant is shown in Table 1.

The force-time curve can be generated analytically if the projectile and cannon properties are known, along with the propellant type and amount of charge, by using the law of combustion, energy conservation law, and the equation of motion for the projectile. Alternatively, it can be established from test results. The area under the force-time curve represents the linear impulse generated by the firing of the mortar and must be absorbed by the mortar baseplate without interfering with the ballistic path required to place the round on target.

As shown best in conjunction with FIG. 5-6, the ball socket 14 is the interface between the mortar cannon and the baseplate 10. For purposes of disclosing the preferred embodiment, and not intended as a limitation, the ball socket 14 can be of the same or similar design as that of the current 81 mm baseplate socket in terms of rotation for alignment with the baseplate stake, insertion of the breech plug, and locking of the barrel. Rather than being machined into the baseplate, the socket 14 can be fastened to the support leg structure 10 by threaded fasteners or rivets, and readily replaced at the organizational maintenance level if need be.

Referring now to FIG. 9-14, a first alternate embodiment of an architecturally design mortar base plate 110 is shown according to the present invention. The base plate 110 is also designed to replace base plate 8 of the PRIOR ART as shown in FIG. 1. The base plate 110 is formed of a composite architectural structure having a center receiving hub 112 and forming a socket 114. The hub 112 is made of one piece machine from one piece machine from solid maranging steel, 4140 Steel, or any structural material for socket to absorb the impact over repeated cycling. A plurality of optimized metal ribs 120 extend radially out from the hub 112 and interlock to form a connection joint 122. The ribs 120 are forging to shaping metal by using localized compressive forces. Such forging additionally decreases corrosion or stress cracking weaknesses by eliminating voids in the material that facilitate such weaknesses or failures. As would be obvious to a person having ordinary skill in the relevant art, in hindsight of the teachings and benefits disclosed by the present invention, the present invention can be readily adapted to cold forging, warm forging or hot forging. Cold forging is done at room temperature or near room temperature. Hot forging is done at a high temperature, which makes metal easier to shape and less likely to fracture. Warm forging is done at intermediate temperature between room temperature and hot forging temperatures.

Forging results in metal that is stronger than cast or machined metal parts. This stems from the grain flow caused through forging. As the metal is pounded the grains deform to follow the shape of the part, thus the grains are unbroken throughout the part.

The forged ribs 120 distribute the recoil and impact strength from the socket 112 to throughout the whole base volume to consume the energy that created due to firing. Alternately, as taught by the related applications referenced above, Kevlar® or structural fabric webs 124 can be affixed additionally between the ribs 120 shares the recoil impact energy to each rib 120 and polymer body.

Referring now to FIG. 15-20, a stabilizer pad 200, anticipated as being formed of a polymeric material, is intended for use in conjunction integrally with any style baseplate 10, 100, and will ultimately transfer the mortar recoil force to ground. The stabilizer pad 200 will act as a hysteresis damper component in the baseplate assembly. The stabilizer 20 pad will be integrated with the support legs and will terminate at the ground in a ring configuration 202. Although shown in FIG. 15-20 as a solid wall structure, other configurations—such as wall cut-outs to reduce weight—are anticipated as obvious improvements of the functions and features described herein. A person having ordinary skill in the relevant art, in light of the present teachings, will be able to evaluated the effects of such modifications on baseplate performance.

It is anticipated that the stabilizer pad 200 is made of a polymeric material, including synthetic rubbers, thermoplastic rubbers, urethanes, etc. In addition to the physical properties required to withstand environmental and operational conditions, key material characteristics will also include the necessary coefficients of stiffness and damping that will lead to an effective mortar baseplate unit.

Given the present teachings and findings, additional functional elements are anticipated within the present invention. Horizontal leg stringers may be added to the leg support structure in order to distribute the transverse force created by the elevation angle of the mortar to each of the support legs and ultimately to the stabilizer pad. The leg stringers will be fabricated from flexible high strength, low elongation material, such as aramid, to minimize weight. The locations, material requirements, and effectiveness of the stringers will be evaluated during design analysis.

2. Operation of the Preferred Embodiment

In accordance with a preferred embodiment of the present invention, the ribs 20 are connected into a joint 26 within the hub 12. The joint 24 is designed to allow for a transfer of motion along with any impact force such that the ribs 10 have a ‘shock absorber’ effect in cushioning the hub 12. The ribs 20 thereby distribute and dampen this force throughout the structure, and allow for the hub 12 to move back to its original position after firing.

The loading on the baseplate assembly under such conditions is shown in FIG. 21. The resultant loads on the baseplate assembly in the z-direction can be accurately modeled by a straightforward spring and damper system, which yields an equation of motion of:

F-Reaction(t)=knzn(t)+cnvn(t)  (1)

Where:

F-Reaction(t) is the reaction force between the baseplate system and ground (This force will be variable over time based on the linear impulse from the mortar, and will have a planar distribution on the stabilizer pad);

kn is the equivalent spring constant of the support legs and stabilizer pad;

zn(t) is the displacement of the support legs and stabilizer pad over time;

cn is the damping fact& of the support legs and stabilizer pad; and

vn(t) is the velocity the support legs and stabilizer pad over time.

In the transverse, or x-direction, the spring-damper characteristics are expected to be less of a factor, and the resistance to the recoil force and overturning moment will be reacted by friction between the stabilizer base and ground, and the weight of the mortar system.

A preliminary finite element analysis performed on the initial concept shows the level of the von Mises stress in one support leg in FIG. 22. This initial concept was based on a rectangular cross section of AISI 4140 alloy steel subjected to vertical loading only. The results show a deflection of 0.262 inch and a maximum stress level of 32,000 psi, well below the 130,000 psi yield stress of heat-treated 4140 steel.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. Therefore, the scope of the invention is to be limited only by the following claims. 

1. An architecturally design mortar base plate for use in combination with an otherwise conventional mortar, said mortar base plate comprising: a center receiving hub forming a socket; a plurality of ribs attached to and extend radially out from said hub; a stabilizer pad formed to receive an assembly of said hub and said ribs, said stabilizer pad for operatively distributing recoil and impact strength exerted at said socket to throughout the whole base volume to consume the energy that created due to firing.
 2. The mortar base plate of claim 1, wherein said stabilizer pad is formed of a material selected from the group comprising: synthetic rubbers; thermoplastic rubbers; urethanes; Kevlar®; polymer mixed with carbon fiber shreds; mesh or polymer resin; metal; ceramic polymer matrix; and other structural fabric.
 3. The mortar base plate of claim 1, wherein said hub is made of one piece machine from any structural steel that includes the toughening by forging, cold working, rolling casting, or other similar metalworking process.
 4. The mortar base plate of claim 1, wherein said ribs are formed of maraging Steel or any structural steel including the toughened by forged, cold working, rolling casting or the like.
 5. The mortar base plate of claim 4, wherein said ribs are connected into a joint formed within said hub, wherein said articulating joint operatively allows for a transfer of impact force energy such that said ribs have a ‘shock absorber’ effect in cushioning said hub.
 6. The mortar base plate of claim 4, wherein said casing encases distributes and dampens force throughout the base plate.
 7. The mortar base plate of claim 7, wherein said ribs are formed of maraging steel, or any structural steel including the toughened by forged, cold or TITANIUM and to achieve the weight reduction.
 8. The mortar base plate of claim 1, wherein each said rib further comprises: a first radially extended leg member opposite a second radially extended leg member; an arcuately opposed receiving joint formed between said first leg member and said second leg member; wherein said receiving joint allows for a transfer of impact force energy such that said ribs have a ‘shock absorber’ effect in cushioning said hub.
 9. The mortar baseplate assembly of claim 1, wherein said stabilizer pad adapted to be reversible useable and having a top surface and a bottom surface, wherein said top surface is configured for engagement with a first ground surface condition and said second surface is configured for engagement with a second ground surface condition.
 10. A modular mortar baseplate assembly comprising, in combination: a ball socket for receiving and retaining a cannon of an otherwise conventional mortar; a support leg structure operatively connected to and supporting said ball socket; and a stabilizer pad in physical communication between said support leg structure and a support surface for transferring a mortar recoil force from said cannon to said support surface.
 11. The assembly of claim 10, wherein said ball socket is fastened to said support leg structure by threaded fasteners or rivets, and thereby adapted to be readily replaced for maintenance or repair as required.
 12. The assembly of claim 10, wherein said support leg structure comprises a structurally engineered multi-legged unit, wherein each support leg comprises a characteristic of a spring for absorbing and distributing a recoil force of the mortar.
 13. The assembly of claim 12, wherein said support leg structure forms a 6-legged hexagonal pattern.
 14. The assembly of claim 10, wherein said stabilizer pad act as a hysteresis damper and integrates with said support legs and terminates at the ground in a ring configuration.
 15. The assembly of claim 14, wherein said stabilizer pad is formed of a material selected from the group comprising: synthetic rubbers; thermoplastic rubbers; and urethanes.
 16. The assembly of claim 15, wherein said stabilizer pad adapted to be reversible useable and having a top surface and a bottom surface, wherein said top surface is configured for engagement with a first ground surface condition and said second surface is configured for engagement with a second ground surface condition. 